Fair Value Disclosures - Financial Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Footnote) (Detail) - USD ($) $ in Millions	Nov. 30, 2014	Dec. 01, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of equity options transferred from Level 1 to Level 2 within Financial instruments owned		$ 6.1
Fair value of equity options transferred from Level 1 to Level 2 within Financial instruments sold, not yet purchased		$ 6.6
Assets at fair value segregated for regulatory purposes	$ 453.7
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Increase corporate debt obligations	33.2
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value segregated for regulatory purposes	$ 545.0